refactor(cheddar): Set up scaffolding for Markdown rendering r/281

Generalises the two bits of the program that will be required either
way (extension parsing and syntax loading).

A dependency on Comrak is introduced as I think GitHub-flavoured
Markdown (with all its fancy extensions) is desirable!

1 files changed, 37 insertions, 11 deletions

diff --git a/tools/cheddar/src/main.rs b/tools/cheddar/src/main.rs
index 9cf85385705d..76bf834cb806 100644
--- a/tools/cheddar/src/main.rs
+++ b/tools/cheddar/src/main.rs
@@ -6,7 +6,8 @@ use std::path::Path;
 use syntect::easy::HighlightLines;
 use syntect::dumps::from_binary;
 use syntect::highlighting::ThemeSet;
-use syntect::parsing::{SyntaxSet, SyntaxReference};
+use syntect::parsing::SyntaxSet;
+use lazy_static::lazy_static;
 
 use syntect::html::{
     append_highlighted_html_for_styled_line,
@@ -14,7 +15,14 @@ use syntect::html::{
     IncludeBackground,
 };
 
-fn syntax_from_args(syntaxes: &SyntaxSet) -> Option<&SyntaxReference> {
+// Set up syntaxes as a lazy_static. Initialisation might not be
+// required in the case of Markdown rendering (if there's no code
+// blocks within the document).
+lazy_static! {
+    static ref SYNTAXES: SyntaxSet = from_binary(include_bytes!(env!("BAT_SYNTAXES")));
+}
+
+fn args_extension() -> Option<String> {
     // The name of the file to be formatted is usually passed in as
     // the first argument and can be used to determine a syntax set.
     let args = env::args().collect::<Vec<String>>();
@@ -22,10 +30,9 @@ fn syntax_from_args(syntaxes: &SyntaxSet) -> Option<&SyntaxReference> {
         return None
     }
 
-    Path::new(&args[1])
-        .extension()
+    Path::new(&args[1]).extension()
         .and_then(OsStr::to_str)
-        .and_then(|ext| syntaxes.find_syntax_by_extension(ext))
+        .map(|s| s.to_string())
 }
 
 fn should_continue(res: &io::Result<usize>) -> bool {
@@ -35,9 +42,11 @@ fn should_continue(res: &io::Result<usize>) -> bool {
     }
 }
 
-fn main() {
-    let syntaxes = from_binary(include_bytes!(env!("BAT_SYNTAXES")));
+fn format_markdown() {
+    unimplemented!("Not able to format Markdown just yet");
+}
 
+fn format_code(extension: String) {
     let stdin = io::stdin();
     let mut stdin = stdin.lock();
     let mut linebuf = String::new();
@@ -49,9 +58,15 @@ fn main() {
     let ts = ThemeSet::load_defaults();
     let theme = &ts.themes["InspiredGitHub"];
 
-    let syntax = syntax_from_args(&syntaxes)
-        .or_else(|| syntaxes.find_syntax_by_first_line(&linebuf))
-        .unwrap_or_else(|| syntaxes.find_syntax_plain_text());
+    let syntax = SYNTAXES.find_syntax_by_extension(&extension)
+        .or_else(|| SYNTAXES.find_syntax_by_first_line(&linebuf))
+        .unwrap_or_else(|| SYNTAXES.find_syntax_plain_text());
+
+    // We're doing a completely different thing if the file is
+    // Markdown, so lets do that thing.
+    if syntax.name == "markdown" {
+
+    }
 
     let mut hl = HighlightLines::new(syntax, theme);
     let (mut outbuf, bg) = start_highlighted_html_snippet(theme);
@@ -63,7 +78,7 @@ fn main() {
     // newlines to be efficient, and those are stripped in the lines
     // iterator.
     while should_continue(&read_result) {
-        let regions = hl.highlight(&linebuf, &syntaxes);
+        let regions = hl.highlight(&linebuf, &SYNTAXES);
 
         append_highlighted_html_for_styled_line(
             &regions[..],
@@ -83,3 +98,14 @@ fn main() {
 
     println!("</pre>");
 }
+
+fn main() {
+    let extension = args_extension()
+        .expect("cheddar should be invoked with a filename!");
+
+    if extension == "md" {
+        format_markdown();
+    } else {
+        format_code(extension);
+    }
+}